The present invention relates to an organic compound useful as a light emitting material for an organic electroluminescence element (hereinafter referred to as an xe2x80x9corganic EL elementxe2x80x9d) and a light emitting material for other electronic device materials or the like, and to an element employing such organic compound.
Organic EL elements are constructed by layering, on a transparent glass substrate, a transparent first electrode (for example, ITO), an organic compound layer which includes an organic compound having strong fluorescence, and a metal (for example, Mg) second electrode in that order.
The organic layer has, for example, a three-layer structure in which a layer of molecules having a hole transport function, a layer of molecules having an emissive function, and a layer of molecules having an electron transport function are layered in that order, and emits light when an electric field is applied to the pair of electrodes. In other words, when holes are injected from the first electrode and electrons are injected from the second electrode, the injected holes and electrons move through the hole transport functional molecule layer, the emissive functional molecule layer, and the electron transport functional molecule layer of the organic layer, such that the holes and electrons collide, recombine, and disappear. The energy generated by there combination is used for producing exited states of the emissive molecules and fluorescence is emitted from the organic EL element.
In such an organic EL element, an aluminum quinolinol complex (Alq3) represented by a chemical formula (3), 
is well known as a light emitting material having a quinoline ring. This compound is obtained by substituting a hydroxy group into the quinoline ring to form a complex with aluminum and emits a green light.
As a red light emitting material for an organic EL element, a phthalocyanine derivative as disclosed in Japanese Patent Laid-Open Publication No. Hei 7-288184 and a porphyrin derivative as disclosed in Japanese Patent Laid-Open Publication No. Hei 9-296166 are known.
Because all of the known light emitting materials having the quinoline ring such as Alq3 have a short conjugate system, light emitting function has so far been obtained only in the bluexcx9cgreen range. To realize a color organic EL element, it is necessary to obtain a compound which emits light with sufficient characteristics for other colors, specifically those in the yellowxcx9cred range.
On the other hand, although the phthalocyanine derivative and porphyrin derivative as described above have a red light emitting function, they do not have sufficient luminance nor sufficient endurance, and, thus, do not satisfy all the requirements desired for applications such as in an organic EL element.
The present invention was conceived to solve the problem described above, and one object of the present invention is to provide a novel organic compound having superior stability and light emitting luminance characteristic and having light emitting function in yellowxcx9cred range, and an organic EL element which employs such organic compound.
In order to achieve at least the object described above, according to the present invention, there is provided a quinoline derivative compound represented by a chemical formula (1), 
wherein at least two of the substituents R1xcx9cR7 in the chemical formula (1) have a structure represented by a chemical formula (2), 
where Q in the chemical formula (2) is an arbitrary functional group.
In the novel organic compound, at least two substituents having a double bond in the structural formula (chemical formula (2)) are introduced as substituents for the quinoline ring (chemical formula (1)). Because of this, the compound has a structure in which the conjugate system is long and the energy difference between the excited state and the ground state of the compound is small and, thus, light emission function in the yellowxcx9cred range can be obtained.
According to another aspect of the present invention, it is preferable that, in the organic compound represented by the chemical formula (1), at least one of the substituents R1xcx9cR7 other than the substituents having a structure represented by the chemical formula (2) is an electron attracting substituent.
By introducing an electron attracting substituent as a substituent in the quinoline ring, the fluorescence quantum yield of the compound can be improved and, as a result, a light emitting material which can emit light at higher luminance and higher efficiency can be obtained.
According to another aspect of the present invention, it is preferable that, in the organic compound, Q in chemical formula (2) is an aromatic group having carbon or aheteroatomin the skeleton of the ring and at least one of the substituents RQ of the aromatic group Q is an electron donating substituent.
By using a stable aromatic group as Q, it is possible to prevent reactions of the double bonds in the chemical formula (2) and thereby improve the stability as a compound. Furthermore, by using at least one electron donating substituent for the substituents RQ, the fluorescence quantum yield of the overall compound represented by the chemical formula (1) can be improved. In particular, it is preferable that an electron attracting group is introduced to at least one of the substituents R1xcx9cR7 of the quinoline ring and an electron donating group is introduced as the substituent RQ of Q. More preferably, a cyano group is used for the subsituent R3 and a p-aminophenyl group is used for the substituent Q. With such a structure, the fluorescence quantum yield of the compound is further improved, and a light emitting material having even higher luminance and higher efficiency can be obtained.
According to another aspect of the present invention, it is preferable that, in the organic compound, the number n of the double bonds in the chemical formula (2) be, for example, at least 2 or no more than 5, or it is also preferable that the number n of the double bonds in the chemical formula (2) be in the range of 1xcx9c3.
When the value of n is in the range of 1xcx9c3 or 2 or greater, a highly stable compound can be obtained which allows for improvements in the endurance of an element when the compound is used, for example, in an organic compound layer of an organic EL element, as will be described below.
According to another aspect of the present invention, it is preferable that the substituents Rn and Rxe2x80x2n in the chemical formula (2) are cyclized. Through the cyclization, free rotation which is normally generated in a vinyl group represented by the chemical formula (2) can be blocked, and the link in the conjugated system can be maintained. Moreover, separation of the n-bonds within the molecule and alteration of the molecular shape can also be prevented, allowing for improvement in the endurance or the like of the molecule.
According to another aspect of the present invention, there is provided an organic electroluminescence element wherein an organic compound layer which includes an emissive layer is formed between two electrodes, and the organic compound described above, that is, an organic compound represented by the chemical formula (1) and having at least two of the substituents R1xcx9cR7 substituted by a substituent represented by the chemical formula (2), is used for the organic compound layer.
As described above, because the organic compound according to the present invention has a light emitting characteristic in the yellowxcx9cred range, by using the organic compound as the material for the organic compound layer, in particular, for the emissive layer, of the organic EL element, an organic EL element having high luminance, high efficiency, and high stability can be obtained.
According to another aspect of the present invention, it is preferable that, in the organic electroluminescence element, the organic compound layer comprises a hole transport layer and an emissive layer, and any one of the quinoline derivative compounds described above is doped into the hole transport layer.
According to another aspect of the present invention, there is provided an organic electroluminescence element wherein an organic compound layer which includes an emissive layer is formed between two electrodes, the organic compound layer comprises a blue emissive layer and a hole transport layer doped with any one of the quinoline derivative compounds as described above, and the organic electroluminescence element emits white light.
As described above, the quinoline derivative compound of the present invention not only demonstrates light emission characteristic of yellowxcx9cred range when used alone, but also produces a light in a similar wavelength range in a hole transport layer when the quinoline derivative compound is doped to the hole transport layer. Therefore, in an organic EL element, light can be emitted having a color determined by the synthesis of the light from the emissive layer and the light from the hole transport layer. For example, by using a blue light emitting material for the emissive layer and the quinoline derivative compound according to the present invention as the doping material of the hole transport layer, it is possible to obtain a white light emitting organic EL element through the synthesis of the blue light from the blue emissive layer and the light in the orangexcx9cred range from the hole transport layer. In such a case, because the synthesized color can be obtained merely by doping the hole transport layer, there is no need to increase the number of emissive layers.
By using, for the organic compound layer of the element as described above, an organic compound in which an electron attracting substituent is introduced to at least one of the substituents R1xcx9cR7 other than the substituents substituted by the substituent represented by the chemical formula (2), an organic EL element can be obtained which has even higher light emitting efficiency or which is capable of being driven at a low voltage. In addition, by introducing an electron donating substituent as a substituent RQ of Q (aromatic group) in the chemical formula (2), further improvements in the light emitting efficiency can be realized.